Heat detecting system



April 12, 1949. 1 EVANS HEAT DETECTING SYSTEM 3 Shets-Sheet 1 FiledApril 25, 19.45

INVENToR. Evan@ April 12, 1949.l 4 1 EVANS I 2,467,120

HEAT DETECTING SYSTEM Filed April 25, 1945 5 Sheets-Sheefl 2 IN V ENTOR.

April l2,v 1949. J, EVANS 2,467,120

HEAT DETECTING SYSTEM Filed April 25, 1945 3 Sheets-Sheet 5 HTTIPIVEYPatented Apr. 12, 1949 2,461,120 HEAT DETECTING SYSTEM John Evans,Hightstown, N. J., assgnor to Radio Corporation of America, acorporation of Dela- Ware Application April 25, 1945, Serial No. 590,293

Claims. (Cl. 1250-833) The present invention relates to infra reddetectors and more particularly to a system having an improved ratio ofsignal to noise In the detection of infra red heat waves by means ofheat sensitive elements it has been found that random noises so impairthe reception as to render a large percentage ofreceived signals eitherunintelligible or undetectable.

An object of the present invention is to provide an improved system fordetecting heat waves.

Another object of the invention is to provide a system wherein signalsheretofore undetectable because of noise are now detectable'.

Another object of the invention is to provide a system wherein a signalis successively detected by a plurality of sensitive heat responsiveelements and translated to a receiving device as a composite signalgiving a magnification of the signal detected by a single heatresponsive element.

A further object of the invention is to provide a scanning device forsweeping the horizon to locate a source of heat arranged in associationwith a unit responsive to heat wave's to generate a plurality ofelectrical pulses in timed Sequence as a function of the sweep of thescanning device, and superposing the pulses to form an output greater inamplitude than any one of the pulses.

Other objects will appear hereinafter.

In the accompanying drawings, Figure 1 represents a side elevation ofone form of heat detecting unit of the invention; Figure 2 represents asection on line 2-2 of Fig. 1; Figure 3 represents a section on line 3-3of Fig. 1; Figure 4 is a diagram of one form of circuit of the presentinvention; Figure 5 is a graph of the time input pulses, taken as anillustration; Figure 6 is a graph of the added output pulses as derivedby the operation of the invention; Figure 7 represents a side elevation,in part section, of one form of scanning mechanism employed inassociation with the system of the present invention; Figure 8represents an end elevation of the heat detecting unit; Figure 9represents a section on line 3-9 of Fig. 7; Figure 10 represents asection on line Ill-I0 of Fig. '7; Figure 11 represents a detail in endelevation of the clutch control switch; Figure 12 represents a sectionon line I2-I2 oi Fig. 11; Figure 13 is a circuit diagram of the clutchcontrol.

Referring to the drawings, one form of the invention comprises aparabolic mirror I0 suitably mounted within a drum II which is rotatableabout a vertical axis in order that the eiective field of the mirror I0can be made to sweep the horizon at a uniform rate. When the mirror IIIintercepts incoming infra red rays, the latter are reiiected to a heatdetecting unit I2 mounted at the focus of the mirror III. This unit I2comprises three thermal elements I3, I4 and I5 mounted in spaced apartrelation but in close proximity within a head IB, in the form of aninsulated ring which is the base or support'of a microlm. The thermalelements I3, I4 and I5 are resistors formed of material having anegative coefficient of temperature when exposed to heat. For example,these resistors are preferably tellurium oxide. The lm includes threecontacts Il, I8 and 20 insulated one from the other and preferably ofgold, and respectively conductively connected to the elements I3, I4 andI5. The periphery of the ring is interrupted by slots 2I, 22 and 23respectively formel in the contacts I1, I8 and 20, to receive mountingscrews 24, 25 and 26 traversing the head I6 and respectivelyconductively connected to terminal pins 21, 28 and 30. A fourth contact3| is conductively connected to the thermal elements I3, I4 and I5 as acommon return for the several electric circuits, and has a peripheralslot 32 to receive a mounting screw 33 leading to the return terminalpin 34. The extended terminals 21, 28, 3U and 34 are supported ininsulated relation by a plate 35 forming an end closure for acylindrical casing 36 which houses the foregoing parts with the head I6closing the opposite end thereof. A heat transparent window 31 formed asa segment of a sphere seals the exposed element end of the contact head,and is preferably formed of silver chloride and serves to direct thereceived heat rays to the sensitive elements. Preferably the exposedface of each of these elements has a coating of heat absorbing material,having a negative coeilicient of resistance, such for` example as ablack conductive oxide.

In order to produce an electrical signal as each element I3, I4 and I5responds to the detected heat, these elements are connected in parallelin a circuit 38 including a source of voltage 43 and suitableresistances 4I respectively in series with the aforesaid elements. Thus,as the axis of the mirror I0 sweeps across a source of heat, thedetecting elements I3, I4 and I5 will suc cessively respond to generatea signal or pulse to be transmitted by way of conductor 42 first,conductor 43 second, and conductor 44 third. For illustration, thesecond pulse from a conductor 43 may follow the iirst pulse byonethirtieth of a second, and the third pulse from 3. the conductor 44may follow the second pulse also by one-thirtieth of a second, ortwo-thirtieths of a second after the first pulse.

Since the three pulses are out of phase as to time and it is desirous ofobtaining an output of the pulses in phase as to time, the signal orpulse transmitted by the conductor 42 is initially amplified byv asingle stage amplifier 45 having an output to the primary of atransformer 46. The secondary of the transformer 46 becomes the input toa time delay network 41, wherein, in the present illustration, thetravel of the generated pulse is delayed two-thirtieths of a secondbefore reaching the output conductor48. Similarlythe pulse transmittedby the conductor 43 is initially amplied by a single stage amplifier l)having an output to the primary of a` transformer 5l. The secondary ofthe transformer 5| becomes the input to a time delay network 52,wherein, inl

the present` illustration, the travel of the generated pulse-isdelayedfone-thirtieth of a 'second before reachingl the' outputconductor llt.. Also, the pulse transmitted. by the conductorxdli isinitially ampliiied by a,y single stage amplier 53 having an output tothe primary of a transformer 54. The secondary of the transformer 54 isdirectly connected by a conductor 55V tothe output conductor llli sothat. the time or phase of the pulse is unchanged. The conductorvd,being common to the. three circuits carries the three pulses` totheprimary ofv a transformer 56, the secondary of which delivers thecombined.` or superposed.` pulses to a two stage amplifier 5l from whichthe added outputleads by the conductor 58 to a control switch 5t" andthence by a` conductor 6Il to theV vertical deectorlplates of an`electron ray tube 63 of the visual type. The necessary deflectingvoltagefor the horizontal plates of the tube 63, as a time factor, is. derivedfromy a potentiometer 64:` included inv a circuit having a source ofvoltage 55. The potentiometer (Mis mechanically connected to follow thescanning movementof the mirror lil as a control for the deflectingvoltage for the horizontal angle indication aswill be hereinafterexplained.

Ashere shown, the scanning drum. ll is: of elongated cylindrical` shapehaving the heat detecting unit mounted coaxially by aspider 66. inposition to locate the heat cells atthe/ focus of the mirror li)4 which,is mounted at or near` the opposite end of the drum il; Scanning motionis transmitted to the drum l I by a vertically disposed shaft B'Imounted inastepbearing 58 and arranged to be oscillated by an armatureclutch disc 'l0 keyedfto the shaft by akey 'H for limited linear motion.As shown, the` disc 10- isY positioned between; two annular solenoids l2and T3 encircling the shaft 6l, the former, 12, having a driven gear 14attached thereto, aswelll as two spaced apart contactorl rings 75, and16,- while the latter, 13, has a driven gear.`y 'Il attached thereto, aswell as two spaced apart contactor rings 18 and 80. Thus, depending uponwhich solenoid is energized,` the shaft (il,` can be swung clockwiseorcounter-clockwise-for a scanning operation.

In order. to transmit continuous'motion to; the two gears 'i4 and 11; amotor IHv is-providecl having a shaft182 driving af pinion 83 in meshwith the gear l1 and also in mesh with a, geary 84 attached to acounter-shaft 85 having a second gear Bt thereon in mesh with thedrivenA gear-14.

For selectivelyenergizing the solenoids 12 and T13-,two contactorsf'land 88v are arranged to. ride upon the respective.' contactor.A ringsV'l5-and, 16

for energizing the solenoid l2, and likewise two contactors and 9| rideupon the respective contactor rings 'I8 and 80. These two sets ofcontactors are in a circuit shown in Fig. i3, and are selectivelycontrolled by a bridge contactor in the form of a rock segment 92slidably carried by a fixed segment 93 mounted upon posts 94 forconcentrically partially encircling the shaft 6.1. At the opposite endsrespectively of the segment 93 are spring contacts 95 and 96 arranged tobe alternately engaged by the bridge contactor 92 at the limit of itsmotion in both directions. Oscillating motion is transmitted to thebridge contactor 92 by two pins 97 and 98 attached to the bridgecontactor S2 and inwardly directed to be inthe path of a pick-up arm H90keyed for movement with the shaft 5l. The pins 91 and 98 arecircumferentially spaced to lbe picked up by the arm H10 near therespective ends of the oscillation of the scanning operation. When thearm |00. engagesV thepin 97 the bridge contacter 92. is moved to engagethe contact 96 to energize one solenoid, and when thearm 00 engages thepin 9.3 the bridge contacter 92 is moved to energize the othersolenoid.V Thus, the arc of swing of` the scanning drum lisautomatically determined by the arcuate position of the pins 97 ,and 98as limit controls.

For controlling the deflection voltage for the horizontal scanangleindication, thev movable arrny of potentiometer 64 mounted on theshaft6'! to oscillate` therewith` thereby to alter the horizontal deiectionsynchronously with the scanning operation. Since lit isundesirable toapply incoming signals to thevertical deection plates of the-tube 53during the return sweep of the scanning drum, a switch lis located inthe path of ya nger E02 attached to the shaft 61 and is timed to engageand close the switch Il at the beginning of the scanning operation andhold it closed until the return sweep of the scanning drum begins, atwhich time the nger E02 is removed and the switch remains open therebyto open the circuit of the vertical deiiection plates.

I claim as my invention:

1. A heat detecting system, comprising a scanning device for locating asource or" energy, means for causing said devicek to sweep through apredetermined angle, a unit responsive to said energy located by saidscanning device for generating a plurality oi electrical pulses in atimed sequence as a function of the sweep-of said scanning device withrespect tov said energy, means for superposing said` pulsesv to form an.output greater than any one ofsaid pulses, and` means responsive tothesuperposed pulses for indicating the presence of said compositepulse.`

1 2. A heat detecting system in accordance with claim 1 characterized,in that the indicating means is operated by a sweep of the scanningdevice in one direction only.

3, A- heatdetecting system, comprising a scanning device for locating asource of heat,.means for causingY said device to scan a selected area,a unit responsive to heat waves` located by said scanning device forgenerating a plurality of electrical pulses in a timed sequence as afunction ofthe sweep` of said` scanning device, means for superposing,said pulses to forman output greater than any one of said pulses, meansresponsive to the superposed pulses for indicating the presence ci` saidcomposite pulse, and .means rendering saidindicating means inoperativeupon a, return sweep of saidscanning device.

4; A heat detecting system, comprising ay scanf ning device for locatinga source of heat, means for causing said device to scan aA selectedarea, a unit responsive to heat waves located by said scanning devicefor generating a plurality of electrical pulses in a timed sequence as afunction of the sweep of said scanning device, means for superposingsaid pulses to form an output greater than any one of said pulses, andmeans including an electron ray tube rendering said indicating meansinoperative upon a return sweep of said scanning device.

5. A heat detecting system, comprising a scanning device for locating asource of heat, means for causing said device to scan a selected area, aunit including a plurality of heat responsive elements for generating aplurality of electrical pulses, said elements being arranged forsuccessive operation in a timed sequence as a function of the sweep ofsaid scanning device, means for superposing said pulses to form anoutput stronger than any one of said superposed pulses for indicatingthe presence of said composite pulse.

6. A heat detecting system, comprising a plurality of heat responsiveelements arranged in spaced relation, a heat reflecting member forfocusing received `heat waves upon said elements, means to move saidmember to sweep a horizontal angle and energize said elements one at atime when said member detects a source of heat, an electrical circuitresponsive to said energized elements to generate a succession of pulsesout of time phase as a function of the rate of sweep of said member, anoutput circuit arranged to receive said pulses, a time delay network forbringing said pulses into phase in said output circuit, and meansactuated by the combined pulse output for indicating the composite ofthe plurality of pulses.

7. A heat detecting system, comprising a plurality of heat responsiveelements arranged in spaced relation, a heat reflecting member forfocusing received heat waves upon said elements, means to move saidmember to sweep a horizontal angle and energize said elements one at atime when said member detects a source of heat, an electrical circuitresponsive to said energized elements to generate a succession of pulsesout of time phase as a function of the rate of sweep of said member, anoutput circuit arranged to receive said pulses, means to deliver thelast of a series of pulses directly to said output, means to delay eachpulse prior to said last pulse by the time interval necessary to bringsaid prior pulses into phase with said last pulse at said output, andmeans actuated by the combined pulse output for indicating the compositeof the plurality of pulses.

8. A heat detecting system, comprising a plurality of heat responsiveelements arranged in spaced relation, a heat reflecting member forfocusing received heat waves upon said elements, means to move saidmember to sweep a horizontal angle and energize said elements one at atime when said member detects a source of heat, an electrical circuitresponsive to said energized elements to generate a succession of pulsesout of time phase as a function of the rate of sweep of said member, anoutput circuit arranged to receive said pulses, a time delay network forbringing said pulses into phase in said output circuit, a cathode raytube having vertical deflecting plates and horizontal deflecting plates,said vertical deflecting plates being included in the circuit of saidoutput, means including a potentiometer for controlling said horizontaldeflecting plates, and means for operating said potentiometer insynchronism with said sweep member.

9. A heat detecting system, comprising a plurality of heat responsiveelements arranged in spaced relation, a heat reflecting member forfocusing received heat waves upon said elements, means to move saidmember to sweep a horizontal angle and energize said elements one at atime when said member detects a source of heat, an electrical circuitresponsive to said energized elements to generate a succession of pulsesout of time phase as a function of the rate of sweep of said member, anoutput circuit arranged to receive said pulses, a time delay network forbringing said pulses into phase in said output circuit, a cathode raytube having vertical deflecting plates and horizontal deecting plates,said vertical deflecting plates being included in the circuit of saidoutput, means including a potentiometer for controlling said horizontaldeecting plates, means for operating said potentiometer in syn.-chronism with said sweepmember, and means to open the circuit of saiddeecting plates on the return of said sweep member.

10. A heat detecting system comprising a scanning drum, a heatreflecting member mounted in said d-rum and adapted to focus receivedheat waves within said drum, a plurality of heat responsive elementsarranged in spaced relation at said focus, means including two solenoidsfor oscillating said drum, means for alternately energizing saidsolenoids, means actuated by said elements for generating a plurality ofelectrical pulses in a timed sequence as a function of the sweep of saidscanning drum, means for superposing said pulses each on the other andmeans for indicating said pulses as a composite pulse.

JOI-IN EVANS.

REFERENCES CITED The following references are of l record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,237,193 Mobsky Apr. 1, 19412,284,345 Schlesman May 26, 1942 2,369,622 Toulon Feb. 13, 19452,392,873 Zahl Jan. 15, 1946 2,410,233 Percival Oct. 29, 1946

